const

const is a very welcomed addition offered by ES6 / TypeScript. It allows you to be immutable with variables. This is good from a documentation as well as a runtime perspective. To use const just replace var with const:

const foo = 123;

The syntax is much better (IMHO) than other languages that force the user to type something like let constant foo i.e. a variable + behavior specifier.

const is a good practice for both readability and maintainability and avoids using magic literals e.g.